1. Field of the Invention
The present invention relates to an excavation tool for use in the excavation of earth and sand such as digging of wells or the construction of foundation piling holes and likes.
2. Prior Art
Conventionally, an excavation tool such as that disclosed in Japanese Patent Application, 1st publication, No. 63-11789 for the excavation of earth and sand is known.
This excavation tool will be explained with reference to FIGS. 1 and 3. The rotational force of hammer cylinder 1 and the impact force of a hammer (not shown) driven by air pressure are imparted to device 2. Two axle holes 2a and 2b are provided, symmetrically with respect to the center of the bottom surface of device 2, in the bottom surface of device 2. Block axles 3a and 3b are inserted in these axle holes 2a and 2b rotatably around their axes. Blocks 5a and 5b, which have roughly semicircular forms with roughly the same diameter as device 2, and into the lead end surface of which a plurality of bits 4 . . . are set, are provided at the lead end part of block axles 3a and 3b. Straight edge surfaces 6a and 6b are provided on blocks 5a and 5b in mutual opposition. By straight edge surfaces is meant parts which are flat surfaces, vertical with respect to the lead end surface. In this excavation tool, when the device 2 rotates in the direction of excavation, the end of one of each of the blocks 5a and 5b projects beyond the outer circumference of device 2 by a fixed excavation amount, and and at this time the straight edge surfaces 6a and 6b of both blocks are in mutual contact and are displaced with respect to the center of device 2.
Furthermore, in this excavation tool, when device 2 rotates in the direction of excavation X by means of hammer cylinder 1, blocks 5a and 5b rotate about block axles 3a and 3b while receiving resistance to excavation, and one of the ends of each of straight edge surfaces 6a and 6b of the blocks 5a and 5b projects beyond the outer circumference of device 2 by a fixed amount. In addition, parts of the straight edge surfaces 6a and 6b are in contact, the rotation of blocks 5a and 5b is stopped; in this state, blocks 5a and 5b receive the rotational force of device 2, earth is excavated by means of bits 4 . . . , and in addition, downward progress is made by means of the impact force of the hammer.
At this time, the excavated earth and sand is separated from the lead end of the excavation tool by expelling from air holes 8a and 8b which are provided in the bottom surface of device 2 the compressed air which is expelled when the hammer piston within hammer cylinder 1 descends, and then this earth and sand is moved to within excavation pipe 9 by way of discharge groove 9a which is provided in device 2, and is then discharged upwardly.
The above excavation tool is inserted deeper into the earth as excavation progresses, so that if it is damaged while in this inserted and extended state, it is difficult to withdraw in order to effect repairs or to replace parts. Accordingly, in this type of excavation tool, a high degree of reliability is required so that no problems occur during excavation.